1. Field of the Invention
The present invention relates to a powder hopper for use with a paint spraying apparatus. More particularly, the present invention is directed to a powder hopper with an internal air assist for agitating the powder within the hopper such that it takes on the properties of a liquid.
2. Description of Background Art
In conventional powder hoppers used for supplying spray applicators in paint spray booths, the hopper generally utilizes a fluidized bed at its bottom. This type of powder hopper is illustrated in FIG. 3. As illustrated in FIG. 3, a fluidized level of powder B can be formed in a powder chamber 14 by providing a compressed air chamber 18 below a permeable membrane 30 which allows the compressed air to pass through the non-fluidized level of powder A and form a fluidized level of powder B. However, this conventional powder hopper is insufficient for providing desired fluidized levels. Accordingly, it has been known in the prior art to use mechanical agitators or air assist devices such as air assist rings for agitating the powder within the hopper such that the powder takes on the properties of a liquid.
A problem with the conventional air assist rings is that eventually the assist rings form agglomerations in the powder and do not provide a continuous fluidizing medium in the powder hoppers.
A mechanical-type agitator is disclosed in U.S. Pat. No. 3,711,022 issued to Witte on Jan. 16, 1973. However, the mechanical agitators are noisy and lead to mechanical fatigue of moving parts. In addition, the mechanical agitator of the Witte patent utilizes an electric motor for driving the agitator. The use of an electric motor in the painting environment presents a considerable risk of explosion due to the combustive properties of the powder. Since movable parts within a powder spray environment must be non-electrically driven, conventional powder hoppers have utilized pneumatic systems for driving the mechanical agitators. Such pneumatic systems consume extensive volumes of compressed air to pneumatically drive the agitators. Accordingly, it is desirable to reduce the number of moving parts associated with a powder hopper system.
It has also been known in the prior art to provide a vertical air pad inside of a material hopper and to blow air outward through the vertical air pad in order to fluidize the material in the vicinity of the vertical air pad. An example of such a vertical air pad is shown in U.S. Pat. No. 3,269,428 issued to Stockel et al. Although the vertical air pad disclosed in Stockel et al is effective for fluidizing material near the vertical air pad, it is still insufficient for preventing agglomeration of material along the walls of the hopper.